T cells, both during development and after maturation, utilize adhesion receptors in the VLA protein family to interact with other cells and with extracellular matrix. From preliminary results it now appears that VLA proteins are not only receptors for substrates or target structures involved in cell positioning and migration, but also can directly contribute to signalling through T cells, and can be functionally modulated in response to signals from T cells. The long term goal of this research is to comprehend this striking two-way connection between VLA proteins and T cell activation events, so that we can have a better overall understanding of T cell development and function. To this goal, [1] we will look at how T cell activation (by antigen, antibodies, esters) results in rapid alterations in VLA protein adhesion to both cell and extracellular matrix ligands. In particular, we will explore how some VLA functions are possibly regulated in opposite directions at the same time. [2) will analyze how VLA protein ligands or anti-VLA monoclonal antibodies (MAb) themselves can directly or indirectly facilitate T cell activation, as measured by proliferation, calcium flux, and lymphokine secretion. The studies mentioned in Aims #1 and #2 will utilize normal T cell clones and lines, T cell receptor (TCR) negative mutants, and TCR reconstituted mutants to assess the connection between VLA proteins and the TCR. [3] In addition, using available alpha and beta subunit cDNA's, we will delete and exchange VLA protein alpha and beta subunit cytoplasmic domains, and then variant VLA's (expressed on T cells) will be tested for i) their ability to be functionally regulated, and ii) their ability to facilitate T cell activation. Thus we will determine the role cytoplasmic domains in the apparent bi-directional signalling between T cells and VLA proteins. [4] To investigate VLA proteins on thymocytes, we will look at their stage- specific expression, ligand-binding functions, and the regulation of these functions.[5] Also, to adequately study VLA proteins on mouse T cells and thymocytes we will generate urgently needed anti-mouse VLA protein MAb. Together these experiments will give important insights into how the various cellular and extracellular matrix ligands of VLA proteins can help to direct an orderly program of T cell development and function.